Up to 400 women and girls are being held in Afghan prisons for "moral crimes" including running away from home to escape beatings or forced marriage according to a study.

Ten years after the toppling of the Taliban government was accompanied by Western promises of a new era of women's rights, the justice system remained "stacked against them at every stage", it found.

Virtually all teenage girls held in prison are accused of immorality, either extramarital sex or running away, and around half of adult women inmates.

Imprisonment for immorality has risen steadily since a supreme court ruling that any woman who runs away from her home and does not immediately go to a close relative or the police should be imprisoned.

The report by Human Rights Watch found many inmates had fled a forced marriage, or violent husbands and in-laws.

In some cases women had been charged with having extramarital sex after being raped or forced into prostitution, it said.

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Kenneth Roth, executive director, said: "It is shocking that 10 years after the overthrow of the Taliban, women and girls are still imprisoned for running away from domestic violence or forced marriage.

"No one should be locked up for fleeing a dangerous situation even if it's at home. President Karzai and Afghanistan's allies should act decisively to end this abusive and discriminatory practice."

Running away is not an offence under the Afghan penal code, but the supreme court advised in 2010 that women and girls who flee their homes should be locked up as a precaution against prostitution and promiscuity.

The court declined to comment on the report.

The United Nations has estimated around three quarters of marriages in Afghanistan are forced and unmarried girls are also sometimes given, or exchanged, to resolve disputes or stand in place of a dowry.

Few women are able to gain divorces. If they run away instead, the husband's family often press for a conviction of extramarital sex as well, as an extra punishment, the report found.

The 120-page report, called "I Had to Run Away" said significant progress had since been made in schooling for girls and allowing women to enter politics, and there had been a fall in maternal mortality.

However bias against them remained rife in the legal system it said.

"Even the most horrific abuses suffered by women seem to elicit nothing more than a shrug from prosecutors, despite laws criminalising violence against women," Mr Roth said.